Once a year, Bartholomew Bones comes to town with a wagonload of treasures, among them ``a sackful of magic jars with mysterious labels--Sundrops, Snowrays, Moonbows, Rainflakes, and Whistling Wind.'' Children line up to purchase the jars, as ``a peculiar kind of luck'' comes from just carrying them around. But Tommy Morgan, a newcomer to town (``On a June afternoon too hot to hurry, he sprang up from nowhere''), insists on opening his bottle of Moonbows. When there seems to be nothing inside, Mr. Bones's wares suddenly lose their appeal. On his way out of town, as ``the dark grew tall in the trees,'' the dejected peddlar empties the jar's contents into a creek, and soon a stunning Moonbow illumines the night sky. Lewis's ( The Tsar & the Amazing Cow ; A Hippopotamusn't ) homely and pungent prose has the ring of a timeless tale handed down through generations. Zimmer ( John Tabor's Ride ) matches this linguistic stylization with some of his best work to date. His eclectically detailed, down-home pictures, firmly rooted in folklore tradition, are the very essence of storybook rusticity. Ages 4-9. ( Mar. )